ABSTRACT Breast cancer is the leading cause of cancer-related death among women on Guam and the Northern Mariana Islands, and Chamorro women have the highest age-adjusted breast cancer mortality rate in the population. The Mariana Islands include Guam and the Commonwealth of the Northern Mariana Islands (CNMI), of which the island of Saipan is the largest and most populated island. No epidemiological or clinical studies have been conducted on Guam or Saipan to study breast cancer risk factors. In this application, we propose to conduct a retrospective case-control study with 200 cases and 400 controls to develop a model of breast cancer risk among Asian Pacific Islanders. Health behavior and obesity measurements will be included. The population will consist of post-menopausal women of predominantly Islands. Data collected from the U-56 Pilot Project II provide preliminary data on behavioral risk factors for cancer among adults on Guam. Poor eating habits, lack of physical activity, and high rate of ovenweight/obesity suggest that many women on aipan Department of Health. Controls will be recruited from patients undergoing screening mammography in several local clinics/facilities and frequencymatched to cases on age and ethnicity. This study, the first large case-control study designed to look at risk factors for breast cancer in women on Guam and Saipan, will provide valuable information that will lead to interventions to reduce breast cancer incidence in these underserved high-risk minority populations. While women in the Mariana Islands appear to exhibit a lower breast cancer incidence than U.S. women generally, availability of mammography is limited. Breast cancer rates are increasing, and high risk of dying from the disease suggests late diagnosis and treatment. In this application, we propose to conduct a retrospective case-control study to develop a model to predict risk of breast cancer in Asian-Pacific Island populations. A long-term goal is to conduct an intervention study to prevent and/or reverse modifiable risk factors associated with breast cancer in the Mariana Islands, using the risk model as a tool to identify highrisk women. Additionally, our risk model could be updated with mammographic density results, if feasible.